Trunnion drive grinding mill



Feb. 1, 1966 E. J. KLOVERS TRUNNION DRIVE GRINDING MILL Original Filed May 27, 1960 1 a Q Q United States Patent 3,232,137 TRUNNHQN BRHVE GRKNDENG MHLL Ervin J. Klovers, Milwaukee, Wis, assigner to Allis- Chairners Manufacturing Company, Milwaukee, Wis. Continuation of application Ser. No. 32,379, May 27, 1960. This application Mar. 20, 1963, Ser. No. 267,385 8 (Ilaims. (Cl. 74-665) This invention relates to a grinding mill and more specifically to a trunnion drive grinding mill including a rotary drum having hollow end trunnions projecting from the drum and mounted in bearing supports and with a drive system connected to one of the trunnions for rotating the drum. This application is a continuation of my copending application Serial Number 32,370, filed May 27, 1960, and now abandoned.

Although it is often fifteen to twenty percent less expensive to build a grinding mill driven by a motor driven pinion that engages a mill ring gear secured around the circumference of the drum, grinding mills are often built with trunnion drives because the latter possesses a number of advantages over the former. The gears of a trunnion drive maybe conveniently arranged within a dust and oil tight gear box thereby making it possible to lubricate the gears with a clean lubricant and keep dust out of the gearing that is one cause of gear wear. Further, the drive system for a trunnion drive mill can be mounted on support means separate from the support means carrying the drum of the mill and therefore differential settling of mill will not result in misalignment of driving gears. A flexible coupling may be provided connecting the drive to the trunnion of the mill to isolate the drive from the efiects of such diiierential settling. Another advantage of a trunnion drive mill is that the gears are isolated from heat generated by grinding within the drum of the mill. Each of these advantages points to the fact that a trunnion drive mill needs less attention and service than a mill driven by a ring gear secured around the circumference of the drum. The added cost of-the trunnion drive mill therefore does not always discourage the selection of this type of mill. This type of mill does however have one disadvantage in addition to cost that in some installations precludes this type of mill being chosen. That additional disadvantage is the length of a trunnion drive mill. Since the drive system extends beyond the end of the drum of the mill, this type of mill is, of course, considerably longer than a ring geardrive mill. One object accomplished by the present invention is to provide a very compact mill arrangement having a minimum length. In fact, the mill that will be hereinafter described is so compact that it is ten feet or more shorter than other currently known and used trunnion drive mills having the same size grinding drum.

Another problem that arose with regard to trunnion drive mills, but one which has already been faced by the prior art, is the problem relating -to the physical size of the gear connected to the trunnion to drive the drum of the mill. In mills of 1250 horsepowerand more, the diameter of this gear approaches the diameter of the drum itself and therefore becomes too large to be practical. The prior .art approached the problem of reducing the physical size of this gear by providing two trains of gears from the driving motor to the gear that is connected to the trunnion. In the usual arrangement these separate gear trains were arranged on opposite sides of the trunnion axis and engaged the gear connected to the trunnion on opposite sides of this gear. Although such arrangements result in reasonable size gears, it is difi'icult to determine if the load is divided equally between the twogear trains. Great care must be taken when aligning these two gear trains to insure that they approach an equal division of the load of turning the drum. Slight cutting errors in making the gears themselves and subsequent gear distortion must be compensated by lapping and wear. Special provisions must be made for handling load that becomes undivided to an extent greater than can be compensated for by wearing in and lapping of the gear teeth. Prior art approaches to this problem have been in the nature of mechanical devices and arrangements 'for moving (i.e., floating or shuttling) gears within the gear box to restore divided load. Among the further objects accomplished by the present invention is to provide for electrically dividing the load between two gear trains externally of the gear box and to provide for an adjustment of such electrical division of the load that can be made without opening the gear box. Further objects accomplished include the elimination of all floating gear mounts and the attendant problems that arise from excessive motion of such gears that amounts to actual bouncing or shuttling of the gears within the gear box.

Generally speaking a preferred embodiment of the pres eut invention will include a first pair of pinions engaging the main gear that is connected to the trunnion. An intermediate gear is connected to each of the pinions to rotate about the same axis as the pinions. A second pair of pinions is provided to drive the intermediate gears. These aforementioned gears are all enclosed within a gear box. Externally of the gear box a pair of synchronous electric motors are provided on the drum side of the gear box with one of the motors driving each of the pinions of the second pair. Means are further provided for adjusting the torque output of at least one of the motors by shifting the angular position of the rotor relative to the stator to provide between each of the motors a substantially equal division of the load of turningthe drum.

Other objects and how they are achieved will appear from the following description when read together with the accompanying drawings, in which:

FIG. 1 is a perspective view of a trunniondrive grinding mill with a top half-of a gear box casing structure removed to show the arrangement of gears within; and

FIG. 2 is a fragmentary view in perspective showing details of one of the electric motors shown in EIG. '1.

Referring to FIG. 1, a trunnion drive grinding mill is shown including a rotary drum 10 having a hollow axial end trunnion 1i projecting therefrom and mounted in a bearing support 12. The bearing support 12 is in turn carried upon a first support means 13 that is part of or connected to foundation structure. Material may be fed to the drum it; through a spout 15. Material fed into the drum 16 through the spout i5 is ground Within-the drum 10 and may be discharged through openings 17 in the trunnion 11.. The drum it) is rotated in a manner and by means that will be described in detail. It issuch rotation of the drum 10 that causes a tumbling action of material within the drum and its reduction in size. Material within the drum 1%) is reduced in the size by the action of the pieces of material on each other and the inner surface of drum 10 both by impact and attrition. In most cases this grinding action is supplemented to a large extent by placing steel balls (not here shown) in the drum iii to tumble with the material and facilitate grinding action. Material discharged from the drum 10 through the openings 17 may be carried away by suitable conveying equipment not here shown.

A drive system 20 is carried by a second support means 21 which like the first support means 13 may form a part of or be connected to foundation structure. However, the second support means 21 is entirely separate from the first support means 13 for reasons that include protecting the engaging teeth of gears that Will be described, from the effects of the normal and expected differential settling of various portions of foundation structure.

The drive system 26 is connected to the hollow trunnion 11. The drive system comprises gears arranged in a gear box 22. As shown, the gear box 22 comprises the lower half of a complete enclosing structure, the upper half of the gear box having been removed of course to more clearly show the arrangement of gears within the gear box. A main driving gear 25 is mounted on a shaft 26. The shaft 26 is journaled in bearing supports 2'7 mounted within gear box 22. The end of shaft 26 on the drum side of the gear box 22 projects through the bearing support 27a and extends in the direction of the drum 1t and its trunnion 11. The shaft 26 is joined to a shaft 2% extending from trunnion 11 by a flexible coupling 30. This flexible coupling 30 may be of any of the conventional designs that are often provided between shafts where torque is to be transmitted from one shaft to another even when the two shafts are not always in perfect axial alignment. There is quite a large number of types of flexible couplings known to this art that would be suitable. Such suitable types include gear, disk, pin, grid, jaw and several others.

Also found within the gear box 22 is a pair of shafts 40 and 40a mounted in bearing supports 41. The shafts 40 and 40a are arranged parallel to and on opposite sides of shaft 26. The first pair of pinions 42 and 42a are mounted on the shafts 4t) and 40a, respectively. The first pinions 42 and 42a both engage the main gear 25 but on opposite sides thereof. A second gear .43, 43a is mounted on each of the first pair of shafts 40 and 40a. Gears 43 and 42 are both secured to the shaft 40 by means not shown so that these two gears rotate together. The same relationship exists between the gears 43a and 42a. A second pair of shafts 44 and 44a are journaled in hearing supports 45 in the gear box 22. The shafts 44, 44a are parallel to and spaced outboard of the first pair of shafts 40 and 40a. A second pair of pinions 46, 46a is mounted on the shafts 44, 44a, respectively, to turn with those shafts. Pinion 46 drivingly engages gear 43 and pinion 46a drivingly engages gear 43a. It should be noted that there are no floating gears in this drive system. That is, each of the bearing supports 27, 41 and 45 are arranged in fixed positions relative to the walls of the gear box 22 and thereby fix a position of the respective shaft axis passing therethrough. As shown on the drawing, each of the gears may be provided with single helical cut type gear teeth. With the position of the axes of the gear shafts being fixed and with the gears meshing through teeth of the single helical type, slight axial movement of the shafts and their gears will be of no consequence and no thrust bearings are required in this arrangement.

A pair of engine type, synchronous electric motors is arranged external to the gear box 22 and on the drum side of the gear box. The term engine type, synchronous, electric motors is generally understood in this trade to refer to synchronous motors of relatively short axial dimension and relatively large diameter having a relatively large number of poles. This designation for this type of synchronous motor resulted from the fact that it was this relatively slow turning type that was first used to replace steam engines of the Corliss and Reynolds types. All engine type motor is also understood to be one comprising a rotor and stator but no shaft or bearings. The rotor of an engine type motor is connected to the shaft of the member shaft it drives. The member shaft is, of course, supported in bearings but the portion of this shaft that supports the motor rotor projects cantilever style to the rotor. This type of synchronous motor is particularly useful in the present invention because it contributes, along with other features, to a very compact design of the mill.

he motors 5i), 5dr: being. of the engine type described above, have rotors that are pressed on to the shafts 44, 44a, respectively, as shown, to drive the pinions 46, 46a and the interconnected gear trains.

As much of the present invention as so far has been described provides division of the load of turning drum fit, this division of load is an electrical division, and this division is external to the gear box 22. To balance the load divided in that manner, one of the synchronous electric motors is provided with a means for adjusting the torque output by shifting the relative angular position of the rotor 51 with respect to the stator 52. The actual division of load between the two synchronous motors 5t? and 5dr: can be easily accomplished, even under no load conditions, by simply connecting an oscillograph to each of the motors and comparing the phase difference shown. After the mill has gone into operation and particularly if it has run long enough to have caused possible unequal wear of gear teeth, the division-of the load may be checked by simply connecting a Watthour meter to each of the motors and comparing those readings. A particularly desirable arrangement for shifting the relative angular position of the rotor 51 and stator 52 is shown in FIG. 2.

FIG. 2 shows an arrangement for shifting the angular position of rotor 51 relative to its stator 52 and shaft 44. This arrangement is disclosed and claimed in a US. Patout No. 3,005,120 issued October 17, 1961, covering the invention of Ward B. Cart and assigned to the a-ssignee of the present invention.

In order to provide the relative motion of the rotor 51 that has been referred to, the rotor 51 is provided with a two part hub assembly comprising parts 53 and 53a. The hub part 53:: is constructed so that it may be turned on shaft 44. The hub part 53 is secured to the shaft 44 as by welding so the hub part 53 turns with the shaft. The hub part 53 is provided with an arm 54 that projects radially outward from shaft 44. An adjusting arm 55 connects the arm 54 to the rotor part 51. Arm 55 is provided with an apertured clevis 56. A bolt 57 passes through the clevis 56 and the arm 54 to secure the adjusting arm 55 to the hub part 53 and shaft 44. The end of adjusting arm 55 that is opposite clevis 56 is provided with a threaded portion 58. The threaded portion 58 is received by an eye 60 of an eyebolt 61. The eyebolt 61 is secured to the rotor part 51 by a nut 62. The threaded portion of arm 55 may slide through the eye 60 to change the distance between the axis of bolt 57 and the axis of bolt 61. As the distance is changed between the axis of these two bolts, rotor part 51 is turned about shaft 44. To secure rotor part 51 in a desired angular position relative to hub part 53 and shaft 44, a pair of nuts 63, 64 are provided on the threaded portion 58 of the arm 55. One of these nuts is on each side of the eye 60 and provides the means for both pushing or pulling the eyebolt 61 and the attached rotor part 51 and hub part 53a relative to arm 55, arm 54, hub part 53 and shaft 44. Nuts 63, 64 further provide the means for holding the desired relationship once it is established by gripping the eye 60 therebetween.

In the operation of the trunnion'drive mill that has been described, material will be fed to the drum 10 through the spout 15, and discharged therefrom through the openings 17 in trunnion 11. To grind the material within the drum 10, the drum is rotated by the drive system 20. The main drive gear 25 is connected to the trunnion 11 through a flexible coupling 30. The main drive gear 25 is driven by two gear trains that divide the load of turning drum 10. Each of the gear trains includes a pinion 46 driven by a motor 50 and therefore turns at relatively high speed and in turn drives a larger diameter gear 43. The gear 43 in turn rotates a smaller gear 42 that acts as another pinion to drive the main drive gear 25. The speed at which pinion 46 turns results in the rotation of gear '43 at a lower speed and a second speed reduction is achieved because the pinion '42 is of smaller diameter than the main gear 25. Both gear trains are shown as being driven by engine type, synchronous, electric motors placed between the drive system 29 and the drum 10. The division of load between the two motors 50 and 504: can be determined easily by merely connecting a watthour meter to each of the motors. Comparing the readings of the watthour meters will indicate the degree to which a load is out of balance "between the two motors. To balance the load between the two synchronous motors, the two nuts 63, 64 shown in FIG. 2 are turned to move arm 55 axially through the eye 60 of eyebolt 61. This motion between arm 55 and eye 60 results in rotor part 51 being shifted relative to shaft 44 and stator 52. As the rotor 51 is shifted relative to the shaft 44 and stator 52, the torque output of the motor is either increased or decreased depending on whether'rotor part 51 is turned clockwise or counterclockwise. In this way the torque output of one of the motors can be changed to balance the torque and load carried by the other motor. Since the load is divided electrically and the division thereof adjusted externally of the gear box 22 all of the shafts 26, 40 and 44 may be mounted in bearing supports that are in fixed positions within the gear box 22. Since no floating gears or pinions are necessary in this design, a more reliable trouble free operation is achieved. Slight axial movement of the gears and pinions in this arrangement can be tolerated and no thrust bearings are required. The arrangement disclosed therefore provides a compact, trunnion drive mill with an easily balanced, divided load drive system with a double speed reduction between the driving motors and the rotating drum.

While but a single embodiment of the invention has been illustrated and described, it will be understood from the foregoing how the objects of the invention have been achieved. Modifications and equivalents such as readily occur to those skilled in the art are included within the scope of this invention which is intended to be limited only by the scope of the claims appended hereto.

Having now particularly described and ascertained the nature of my said invention and the manner in which it is to be performed, I declare that what I claim is:

1. A drive system for trunnion driven grinding mills and the like, comprising, a trunnion gear mounted on a shaft adapted to transmit driving torque, two electric motors arranged axially parallel with the axis of the trunnion gear shaft and with said axis between said motors, each motor having a rotor drivingly connected on one axial end to the trunnion gear through separate gearing, and in which: both motors are on one and the same side of the trunnion gear, each motor has a stator with an axial length shorter than its diameter, and each said rotor being cantilever supported solely on said end connected to said trunnion gear.

2. An apparatus comprising a drive according to claim 1, a trunnion driven machine assembly, a flexible coupling connecting said machine assembly and the trunnion gear shaft, and support structure for the motors and trunnion gear which is separate from said machine assembly.

3. A drive system for trunnion driven grinding mills and the like, comprising, a trunnion gear mounted on a shaft having one end adapted to transmit driving torque, two electric motors arranged axially parallel with the axis of the trunnion gear shaft and with said axis between said motors, each motor having a rotor drivingly connected on one axial end to the trunnion gear through separate gearing, and in which: both motors are on the same side of the trunnion gear as said torque transmitting end of said trunnion gear shaft, each motor has a stator with an axial length shorter than its diameter, and each said rotor being cantilever supported solely on said end connected to said trunnion gear.

4. An apparatus comprising ,a drive according to claim 3, a trunnion driven machine assembly, a flexible coupling connecting said machine assembly and the torque transmitting end of the trunnion gearshaft, and support structure for the motors and trunnion gear which is separate from said machine assembly.

5. A drive system for a trunnion driven machine comprising: a main trunnion driving gear; a first pair of shafts arranged parallel to and with one on each side of the trunnion axis; a first pair of pinions with one mounted on each of said first pair of shafts, said first pinions engaging said main gear; a second gear mounted on each of said first pair of shafts and drivingly connected to said pinion mounted thereon; a second pair of shafts parallel to and spaced outboard of said first pair of shafts; a second pair of pinions with one mounted on each of said second pair of shafts, each of said second pinions drivingly engaging one of said second gears; and a pair of engine type synchronous electric motors with each having a rotor cantilever connected to one of said second pair of shafts to drive said pinion mounted thereon.

6. A drive system for a trunnion driven machine comprising: a main trunnion driving gear; a first pair of shafts arranged parallel to and with one on each side of the trunnion axis; a first pair of pinions with one mounted on each of said first pair of shafts, said first pinions engaging said main gear; a second gear mounted on each of said first pair of shafts and drivingly connected to said pinion mounted thereon; a second pair of shafts parallel to and spaced outboard of said first pair of shafts; a second pair of pinions with one mounted on each of said second pair of shafts, each of said second pinions drivingly engaging one of said second gears; and a pair of synchronous electric motors each having a stator with an axial length shorter than its diameter with each having a rotor cantilever connected to one of said second pair of shafts on the trunnion side of said main gear and connected to drive said pinion mounted thereon.

7. A drive system for a trunnion driven machine comprising: a gear box; a main trunnion driving gear mounted on a shaft journaled in said gear box; a first pair of shafts journaled in said gear box and arranged parallel to and with one on each side of the trunnion axis; a first pair of pinions with one mounted on each of said first pair of shafts, said first pinions engaging said main gear; an intermediate gear drivingly connected to each of said first pair of pinions; a second pair of shafts journaled in said gear box parallel to said first pair of shafts; a second pair of pinions with one mounted on each of said second pair of shafts, each of said second pinions drivingly engaging one of said intermediate gears; each of said shafts being journaled in said gear box by being mounted in bearings that are located in fixed positions relative to walls of said gear box; and a pair of synchronous electric motors external of said gear box and each having a stator with an axial length shorter than its diameter with each having a rotor cantilever connected to one of said second pair of shafts to drive said pinion mounted thereon.

8. A drive system for a trunnion driven machine comprising: a gear box; a. main trunnion driving gear mounted on a shaft journaled in said gear box; a first pair of shafts journaled in said gear box and arranged parallel to and with one on each side of the trunnion axis; a first pair of pinions with one mounted on each of said first pair of shafts, said first pinions engaging said main gear; an intermediate gear drivingly connected to each of said first pair of pinions; a second pair of shafts journaled in said gear box parallel to said first pair of shafts; a second pair of pinions with one mounted on each of said second pair of shafts, each of said second pinions drivingly engaging one of said intermediate gears; each of said shafts being journaled in said gear box by being mounted in bearings that are located in fixed positions relative to walls of said gear box; and a pair of synchronous electric motors external of said gear box with each motor having a stator with an axial length shorter than its diameter and each having a rotor cantilever connected to one of said second pair of shafts on the trunnion side of said main gear to drive said pinion mounted thereon.

References Cited by the Examiner UNITED STATES PATENTS Cart 310209 DON A. WAITE, Primary Examiner. 

1. A DRIVE SYSTEM FOR TRUNNION DRIVEN GRINDING MILLS AND THE LIKE, COMPRISING, A TRUNNION GEAR MOUNTED ON A SHAFT ADAPTED TO TRANSMIT DRIVING TORQUE, TWO ELECTRIC MOTORS ARRANGED AXIALLY PARALLEL WITH THE AXIS OF THE TRUNNION GEAR SHAFT AND WITH SAID AXIS BETWEEN SAID MOTORS, EACH MOTOR HAVING A ROTOR DRIVINGLY CONNECTED ON ONE AXIAL END TO THE TRUNNION GEARS THROUGH SEPARATE GEARING, AND IN WHICH: BOTH MOTORS ARE ON ONE AND THE SAME SIDE OF THE TRUNNION GEAR, EACH MOTOR HAS A STATOR WITH AN AXIAL LENGTH SHORTER THAN ITS DIAMETER, AND EACH SAID ROTOR BEING CANTILEVER SUPPORTED SOLELY ON SAID END CONNECTED TO SAID TRUNNION GEAR. 